Jean Asselineau

The biosynthesis of mycolic acids by Mycobacteria: current and alternative hypotheses.

Experimental observations, accumulated during several decades, have allowed an overall scheme for the biosynthesis of the mycolic acids, which are very long chain fatty acids of Mycobacteria to be proposed. But, in almost every step, several hypotheses are compatible with the experimental results, leading to variations of the overall scheme. The aim of this review is to point to some additional possibilities. It is generally assumed that the classical elongation process of fatty acid synthesis produces two long chains, the condensation of which leads to the direct precursors of mycolic acids. But three condensations of four fatty acids, usually synthesized by Mycobacteria, is another hypothesis that could be considered. In the first hypothesis, some methyl or methylene substituents or oxygenated functions are added to the double bonds of an unsaturated precursor, whereas in the second hypothesis, the methylations could help in the building of very long aliphatic chains, and determine the location of double bonds or ramifications. The hypothetical coexistence of two pathways for mycolate biosynthesis is discussed.

Sur la constitution chimique des acides mycoliques de deux souches humaines virulentes de Mycobacterium tuberculosis

1. 1. Mycolic acid, which makes up 8.3% of the dry weight of the human tubercle bacillus Test, can be separated by chromatography into two acids (α and β) which are probably isomers. 2. 2. The elementary analysis of these two mycolic acids and a number of their derivatives confirms the molecular formula C88H176O4 proposed by R. J. Anderson in 1938. Taking into account the difficulties inherent in the analysis of compounds of high molecular weight, this formula can be considered only as being the most probable. 3. 3. Specific reactions show that the hydroxyl group present in the mycolic acids is in the β-position with respect to the carboxyl group. 4. 4. The mycolic acids of the two virulent tubercle bacilli studied here have in the α-position an unbranched side chain containing 24 carbon atoms. The pyrolysis of mycolic acid, investigated by R. J. Anderson, which leads to n-hexacosanoic acid is thus explained. It is a reaction characteristic of β-hydroxy-acids having a side chain in the α-position. 5. 5. Mycolic acids, at least one of which is present in all the strains of Mycobacteria examined up to now, may be defined as β-hydroxy-acids of high molecular weight which contain a long aliphatic side chain in the α-position. This is a completely new aspect in the chemistry of the natural fatty acids.

Chemical structure and biochemical activity of cord factor analogs: II. Relationships between activity and stereochemistry of the sugar moiety

Summary The steric requirement for the toxic activity of cord factor was studied by synthesizing several stereoisomers of methyl 6-mycoloyl-α-D-glucopyranoside and determining their toxicity for mice and the action on the mitochondrial oxidative phosphorylation. Methyl 6-mycoloyl-β-D-glucopyranoside (LD50 = 199 μg) was as toxic as the α-anomer and affected in vitro the mitochondrial oxidative phosphorylation as did the latter. Methyl 6-mycoloyl-α-D-mannopyranoside was slightly toxic and exhibited a slight activity on the mitochondrial oxidative phosphorylation. Methyl 6-mycoloyl-α(?)-D-allopyranoside and -α-D-galactopyranoside were completely devoid of toxicity (LD50 > 500 μg) and did not affect mitochondrial oxidative phosphorylation. These results indicate that the steric disposition of the hydroxyl groups at carbon atoms 2, 3 and 4 of methyl 6-mycoloyl-glucosides play a definite role in the toxicity, while the glycosidic linkage at carbon atom 1 has no specificity.

Etude des phospholipides de Pseudomonas solanacearum présence d'acides gras α-hydroxylés monoéthylénïques

Abstract The phospholipids isolated from Pseudomonas solanacearum consist mainly of cardiolipids and phosphatidyl-ethanolamine. This last fraction can be separated into two fractions, one of which contains only non-hydroxylated fatty acids and the other one a mixture of hydroxylated and non-hydroxylated fatty acids. Non-hydroxylated fatty acids consist of hexadecanoic acid, Δ 9,10 -hexadecenoic acid, Δ 11,12 -octadecenoic acid and a C 17 cyclopropane fatty acid, the structure of which has been established as 9,10-methylene-hexadecanoic acid. The hydroxy acid fraction is a mixture of 2-hydroxy-hexadec-9-enoic and 2-hydroxy-octadec-11-enoic acids, accompanied by low amounts of isomers having the double bond one carbon further from the carboxyl end.

Composition des lipides complexes de Flavobacterium meningosepticum

Abstract The free lipids of Flavobacterium meningosepticum were separated by thin layer chromatography, and the main lipid fractions were analysed by FAB (fast atom bombardment) mass spectrometry. The major products were di-iso-C 15 - and iso-C 15 -iso-C 17 -phosphatidylethanolamine, and two ninhydrine + and phosphorus − fractions. The structures of the latter two fractions were established as ornithine lipids by using MIKE (mass ions kinetic energy) mass spectrometry, GC/MS (gas chromatography coupled with mass spectrometry) and conventional methods. The presence of small amounts of sphingolipids with C 17 - and C 16 -sphinganines was demonstrated. F. meningosepticum can be distinguished from F. multivorum and F. spiritivorum by easy characterization of the ornithine lipids by thin layer chromatography.

Dicorynomycoloyl trehalose activity: Comparison of the activity of α,α′- and β,β′-trehalose derivatives on mitochondrial oxidative phosphorylation

Summary 6,6′-Dicorynomycoloyl esters of α,α′- or β,β′-trehalose were synthesized and tested on isolated rat liver mitochondria. In contrast to the well known site-II-specific uncoupling effect of the α,α′-trehalose derivative, the β,β′-trehalose derivative exhibited only non-specific inhibition of active respiration in the presence of glutamate. It is proposed that this unexpected difference between the two isomers could arise from conformational differences in the carbohydrate moiety of the glycolipids, which would render the β,β′ isomer unable to recognize targets specific to the α,α′-trehalose glycolipid.

Fatty acid composition of the lipids of Pseudomonas mildenbergII: Presence of a fatty acid containing two conjugated double bonds

The whole cell fatty acids of Pseudomonas mildenbergii were extracted and separated, as methyl esters, into non-hydroxylated (60.6%) and hydroxylated (39.4%) esters. The main component of the hydroxy-ester fraction was methyl 3D-hydroxydecanoate. The non-hydroxylated fraction mainly consisted of methyl 2-decenoate, the methyl ester of a C-12 acid having two conjugated double bonds, methyl palmitate, methyl methylene-hexadecanoate and methyl vaccenate.